This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Blowout preventers (BOPs) are used extensively throughout the oil and gas industry. Typical blowout preventers are used as a large specialized valve or similar mechanical device that seal, control, and monitor oil and gas wells. The two categories of blowout preventers that are most prevalent are ram blowout preventers and annular blowout preventers. Blowout preventer stacks frequently utilize both types, typically with at least one annular blowout preventer stacked above several ram blowout preventers. The ram units in ram blowout preventers allow for both the shearing of the drill pipe and the sealing of the blowout preventer. A blowout preventer stack may be secured to a wellhead and may provide a safe means for sealing the well in the event of a system failure.
In a typical annular blowout preventer 100, such as shown in FIG. 1, the annular blowout preventer 100 includes a housing 102 with a bore 120 extending therethrough that is disposed about a longitudinal axis 103. A packing unit 105 is disposed within the annular blowout preventer 100 about the longitudinal axis 103 such that an axis of the packing unit 105 may be aligned or concentric with the axis 103. The packing unit 105 includes an elastomeric annular sealing element 107 and a plurality of metallic inserts 109. The metallic inserts 109 are disposed within the elastomeric annular sealing element 107 of the packing unit 105 and may be distributed at equal radial distances from one another about the longitudinal axis 103. The packing unit 105 includes a bore 111 concentric with the bore 120 of the blowout preventer 100.
The annular blowout preventer 100 is actuated by fluid pumped into an opening 113 of a piston chamber 112. The fluid applies pressure to a piston 117, which moves the piston 117 upward. As the piston 117 moves upward, the piston 117 translates force to the packing unit 105 through a wedge face 118. The force translated to the packing unit 105 from the wedge face 118 is directed upward toward a removable head 119 of the annular blowout preventer 100, and inward toward the longitudinal axis 103 of the annular blowout preventer 100. Because the packing unit 105 is retained against the removable head 119 of the annular blowout preventer 100, the packing unit 105 does not displace upward from the force translated to the packing unit 105 from the piston 117. However, the packing unit 105 compresses inward from the translated force, which compresses the packing unit 105 toward the longitudinal axis 103 of the annular blowout preventer 100. In the event a drill pipe is located along the longitudinal axis 103, with sufficient radial compression, the packing unit 105 will seal about the drill pipe into a “closed position.” In the event a drill pipe is not present, the packing unit 105, with sufficient radial compression, will completely seal the bore 111 by sealing against itself.
The annular blowout preventer 100 may go through an analogous reverse movement when fluid is pumped into opening 115 of the piston chamber 112. The fluid translates downward force to the piston 117, such that the wedge face 118 of the piston 117 allows the packing unit 105 to radially expand to an “open position.” Further, the removable head 119 of the annular blowout preventer 100 enables access to the packing unit 105, such that the packing unit 105 may be serviced or changed if necessary. Alternatively, the packing unit 105 may radially expand to the open position from the elastomeric body 107 biasing and pushing against the piston 117 when the piston 117 no longer applies a pressure to the packing unit 105, thereby enabling the packing unit 105 to expand and relax.
As annular blowout preventers may rely on the use of a piston 117 or some other vertical type of actuation, this may increase the height for the annular blowout preventer. Further, an annular blowout preventer is typically included within a stack, which even further increases the height requirement when installing equipment for pressure control purposes of a well. However, in certain environments and areas, the overall height available may be limited, such as due to the size restrictions when moving equipment on a platform or derrick, or to help protect the fishing industry in areas such as the North Sea. Accordingly, improvements may be made to current designs used for annular blowout preventers.